The present invention is directed to signal sources, and especially to frequency sources generating stable frequency signals across a variety of ambient temperature conditions.
Signal generators designed to generate stable-frequency source, or supply, signals are known. Analog devices, such as crystal oscillators, used in such stable-frequency signal generators render such devices susceptible to variance in output frequency, especially in response to changes in ambient temperature. Prior art stable-frequency signal generators employ expensive oscillator circuitry, insulated circuit modules, temperature compensating circuitry, and other additional packaging or circuitry to seek to generate stable-frequency signals over a range of ambient temperatures. Such compensating packaging, or circuitry, or both are expensive and sometimes bulky. In these times of market pressures to reduce cost and size of electronic components, both results are undesirable.
There is a need for a stable-frequency signal generator, which is inexpensive and not burdened with additional bulk or cost because of insulating packaging or temperature-compensating circuitry.
An apparatus for generating a supply signal at a predetermined frequency comprises a digital synthesizer connected with an oscillator and a processor; and a temperature sensor connected with the processor. The oscillator provides a periodic excitation signal to the synthesizer, which responds by recurrently accumulating bits in quantum bit step amounts to a maximum bit capacity and returning to a starting bit count in a bit accumulating period. The synthesizer generates the supply signal based upon the bit accumulating period. The processor provides a control signal to the synthesizer to control the quantum bit step amount. The temperature sensor and the processor cooperatively employ a predetermined temperature parameter-correction factor relationship to adjust the control signal to set the quantum bit step amount to establish the bit accumulating period appropriately for the predetermined frequency. The method of the present invention comprises the steps of: (a) in no particular order: (1) providing a correlation base correlating a temperature indicator parameter with a correction factor, (2) providing a temperature sensor, (3) providing a processor; (b) sensing a parameter of ambient temperature; (c) generating the temperature indicator parameter appropriate for the parameter of ambient temperature sensed; (d) cooperatively operating the temperature sensor and the processor with the correlation base to determine a correction factor; and applying the correction factor to the synthesizer to affect the quantum bit change to alter the bit accumulating period appropriately to drive the synthesizer toward generating the source signal at the predetermined frequency.
The correlation base may take any form which reliably relates a parameter associated with ambient temperature with a correction factor to be applied for driving the signal synthesizer toward generating a signal at a predetermined frequency. For example, the correlation base may be a table enabling one to enter with the parameter related to ambient temperature and determine the appropriate correction factor. Another form of correlation base may be an algorithmic relation between the parameter related to ambient temperature and a correction factor, with the correction factor expressed as a function of the parameter measured. Other forms of correlation base may easily be applied for use with the present invention and are within the scope of the invention.
The temperature sensor may be connected with the processor via a weighted combining device, which may also receive an input signal from the oscillator. The weighted combining device may then weightingly combine signals from the temperature sensor and the oscillator to produce a weighted indicator of the parameter associated with ambient temperature. This is a useful alternate embodiment because oscillators are affected by temperature change. That change provides another indicator of a parameter associated with temperature independent of the temperature sensor. Properly recognizing the temperaturexe2x80x94toxe2x80x94change relation associated with the oscillator, and properly weighting it with respect to the output received from the temperature sensor, can increase accuracy and reliability of temperature-related information provided to the processor.
Another benefit of either embodiment describedxe2x80x94with or without weighted combined signalingxe2x80x94is that the present invention provides an on-board indication of ambient temperature which may be used elsewhere in a product or system using the present invention. Often products may beneficially use such ambient temperature information, but cannot have it available without additional circuitry to provide it. Increased cost and size resulting from providing such additional circuitry dictates against such features. Employing the present invention for source signal stabilization provides the added benefit of such on-board temperature information xe2x80x9ccost freexe2x80x9d. Such temperature information may be provided, for example, for such activities as temperature alarms, interrupts or similar functions. The processor of the present invention could, for example, be interrogated by other systems in a product for temperature information which may be employed in a myriad of ways. The point is that such on-board temperature information has not previously been available in calibrated form without prohibitively expensive additional circuitry provided for no other purpose than to provide such information. With the present invention, such calibrated temperature information is available relatively xe2x80x9ccost-freexe2x80x9d; no significant additional circuitry is required to enjoy the availability of such temperature information. It is a xe2x80x9ctwo birds with one stonexe2x80x9d result that makes for good engineering.
Yet another benefit of employing the present invention in a product is that any derivative clocks based upon the clock signal stabilized using the present invention will also be stabilized. Further, a system clock in a product, or system, can support multiple signal synthesizing devices, such as the digital synthesizing device employed in the preferred embodiment of the present invention. Yet there only needs to be one temperature sensor and one processor to stabilize all of the on-board signal generating devices of a system.
A still further additional benefit of employing the present invention in a product or system is that compensated clock information yielded by the present invention can be available to other functions within the product or system. Such a stable clock signal would likely be useful for hardware or software timing function.
The invention may also further include an additional correlation capability reflecting the effect of aging upon the apparatus. Thus, there may be a facility for storing an initial date and for determining a present datexe2x80x94or some other means for determining elapsed timexe2x80x94and an age-related correlation base for determining an age-compensating correction factor to the signal synthesizer. The age-related correlation base may also take on any format relating elapsed time with an appropriate correction factor and remain within the scope of the present invention.
It is, therefore, an object of the present invention to provide an apparatus for providing a source signal at a predetermined frequency which is inexpensive to produce.
It is a further object of the present invention to provide an apparatus for providing a source signal at a predetermined frequency which requires no special packaging or insulation.
It is yet a further object of the present invention to provide an apparatus for providing a source signal at a predetermined frequency which does not require temperature-compensating circuitry.
It is a still further object of the present invention to produce a method for generating a frequency-stable signal which does not rely upon special packaging or temperature-compensating circuitry associated with an oscillator device.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.